We use cookies to ensure we give you the best experience on our website. You can find out about our cookies and how to disable cookies in our Privacy Policy. If you continue to use this website without disabling cookies, we will assume you are happy to receive them. Close.

Arch bridges consist of a load-bearing arch in a state of compression, the strength and stability of which allows them to carry greater loads than beam bridges. The arch can support the horizontal deck of the bridge either from above or below.

Where there are suitable support points available, multi-span bridges may be used to create long bridges, and these may include combinations of beam, arch and suspension spans.

Moveable bridges are moveable variations of the three basic forms, generally used in situations where greater headroom under the bridge is sometimes necessary, for example to allow the passage of a ship underneath. The most common types of moveable bridge are:

If the bridge is to span water, barges or pontoons may be used to float materials out to the lifting position. A temporary system of trestles may be used as a means of placing the beams or girders. For bridges spanning high drops, plate-girders or trussed-girders may be hauled across the opening using rollers. Alternatively, cantilever launching may be used, where the beam is launched from one bank, with sufficient ballast to counteract the overturning force, and hauled across the span using a winch.

Cantilevering the ribs out from the sides of the span. This is suitable for bridges over high drops which cannot be spanned with trestles.

Where the spans are very large, the arch may be cantilevered in sections using a creeping crane that is mounted on top of the arch. The crane lifts rib sections from barges or pontoons below. The bridge deck is then constructed from both ends, meeting in the middle.

Bridge bearings provide a resting surface between supporting piers and the deck. They act to reduce the stresses that are involved by allowing controlled movement. They are usually made of metal or flexible materials such as rubber or plastic laminates.

Early suspension bridges were susceptible to vibration when an external periodic frequency matched the bridge's natural structural frequency. This could cause it to become structurally unstable and ultimately could cause catastrophic collapse.

Famously, this is why marching soldiers 'broke step' as they crossed certain bridges. Broughton Suspension Bridge collapsed in 1831, and more recently, Tacoma Narrows Bridge collapsed in 1940. Whilst modern suspension bridgedesign should eliminate such instability, in 2000, the Millennium Bridge in London began to vibrate when large crowds walked across it on its opening. It had to be closed for a year whilst dampeners were designed and installed.

In 2007, an eight-lane, steel-truss-arch bridge across the Mississippi River collapsed killing 13 people. Subsequently, a 2016 report by the American Road & Transportation Builders Association (ARBTA) suggested that almost 10% of America's bridges were in need of repair, that is, they achieved a score of four or less out of nine, when assessed by federal engineers.